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Understanding Soil Types

Why do I need to understand the Soil Types?: Understanding the type of soil you have is essential to plan your Interlocking Concrete Pavers (ICP) project properly. Different soils have different load-bearing abilities. Depending on the type of soil you have may mean more excavation or the addition of extra materials to ensure that your project doesn't settle or heave from frost.

There are Three Types of Soil Classifications:

1. Sand and/or Gravel: Sand and/or Gravel generally has less than 30% fines; this means that water will drain through quickly and not stay and cause issues. You can identify sand and/or gravel by adding water. If it falls apart and does not stay clumped, then it is a good sandy load-bearing soil.

2. Silty Soil: Silty soil is classified as a weak type of soil as it generally has more than 30% fines. When dry, it is a very fine, dusty soil. When wet, it becomes slimy, which obviously makes for a poor structural base. The silty soil is also prone to holding water, which will heave and cause surface issues to your pavement surface during freeze-thaw cycles.

3. Clay: Clay is also classified as a weak type of soil. When dry, it is hard and compact, but when wet, it becomes greasy and holds water; this is bad because it weakens under load and is more exposed to freeze and thaw cycles. Clay is generally found in areas such as Pineview and Beaverly.

I have a "Weak" Soil. What do I do?: Don't be alarmed; having a weak soil type does not mean that you cannot complete your project. It just means that you will need to do a little extra work. Ways to improve the strength of the soils:

  • Amend Soil Chemically: Adding Lime or even Portland Cement to the top of your sub-grade soil changes the soil's chemical composition so that instead of the water getting trapped, it is released from the soil structure.

  • Ensure Proper Drainage: Water is the enemy when you have a silty or clay soil. So you will want to make sure the water does not sit and stay with the soil. Creating a slight slope on your sub-grade soil during excavation will direct the water away from the project. You may also need to install a perforated drain pipe to collect the water and direct it further away from the project.

  • Compact the Soil: If the soil is dry, you can run a plate compactor over the soil. This helps increase the density of the soil and will help keep water out.

  • Adding a ¾" Clean Blasted Rock: Spreading thin layers, 1-2" of ¾" clear rock and then compacting will help in decreasing the ratio of fines in your sub-grade soil. Repeat this step until the soil no longer accepts that stone.

  • Install a Geotechnical Fabric: Installing a Geotechnical Fabric, such as woven or non-woven, that is a minimum 4-ounce weight, will ensure that the sub-grade soil does not mix and work its way into your structural base course. For added structural strength, use a biaxial fabric, although much more expensive, this will significantly increase your pavement structure's strength and help distribute the load.

  • Increase the Thickness of your Base Structure: Increasing the thickness of your base structure also means increasing the depth of excavation. Both of these begin to add to the cost of the project. Although we are not Geotechnical Professionals, we generally recommend at least 8-12" of structural base gravel instead of the 4-6" for sand and gravel soils.

The above are just a few options, and you will likely not need to do all of them for your project. Be sure to ask an expert when planning your project.

Feel free to contact us at Island Cache Stone Company for any questions or design ideas. We are more than happy to show you around the yard and demonstrate how to use any products.

About the Author: Cory Klein is a Co-Founder and Chief Excellence Officer for Island Cache Stone Company. He has an extensive background in Civil Construction and Hardscape Landscaping. He also owns and operates a Hardscape Landscaping business called Northern Earthworks Solutions.

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